２０２４アルミニウム合金４２３Ｋ時効材における初期急速硬化の起源

Abstract

In order to reveal the origin of the initial rapid hardening of Al–Cu–Mg alloys, stress-strain response under various tensile loading conditions was investigated in a 2024 aluminum alloy aged at 423 K (15O°C). Cyclic tensile loading at 77 K resulted in no significant change in stress-strain response. On the other hand, yield-point phenomena evidently appeared in the specimen tested at room temperature. In addition, reduced flow stress was obtained at a higher strain rate in the room-temperature strain-dip test. These experimental findings supported the idea proposed by Ringer et al. that the interaction between dislocations and solute atoms (or co-clusters) was responsible for the initial rapid hardening. However, the idea cannot explain the large stress gain during the initial hardening. Microstructural change at the early stage of aging was examined using TEM. A uniform dispersion of dislocation loops was evident from the very early stage of aging and it remained during the initial hardening stage. Simple calculation based on Orowan mechanism indicated that the existence of dislocation loops resulting from quenched-in excess vacancies was the predominant reason for the initial hardening.